1. Field of the invention
The invention concerns a bellows type sealed transmission device suitable for controling a high-security valve which is operated by a quarter-turn rotation or less. The invention is directed to simplifying the structure of this type of device and to improving the working conditions of the bellows in order to increase its reliability and durability.
2. Description of the prior art
There is a known metal bellows type sealed control device designed to be associated with a valve mechanism, the bellows isolating the mechanism from the external environment. A device of this kind has been developed for the requirements of the nuclear industry, for controling a valve that may be in contact with a toxic and radioactive fluid. This device comprises a control shaft and a receiver shaft isolated from each other. The bellows is disposed to surround the receiver shaft completely and it is welded in a sealed way by its axial ends to a fixed part of the casing of the device, on the one hand, and to a mobile transfer member coupled both to the receiver shaft and to the control shaft, on the other hand. For the bellows to be durable in exercizing its function, it is essential that it is not subjected to any torsion force. This is why the transfer member, which is generally flat, is constrained to move in such a way as to perform a so-called "circular-translation" movement. This movement may be obtained positively by an appropriate kinematic system or in a "resultant" way by virtue of various mechanical prohibition means. The former is preferable but generally requires complicated and costly mechanisms. Devices of this kind are described, for example, in British Patent No. 826 513 and in Patent of Addition No. 78 358 to French Patent No. 1 248 634 which corresponds to U.S. Pat. No. 3,082,632 issued to Vulliez on Mar. 26, 1963. This Patent of Addition describes an embodiment which is particularly suited to controling a quarter-turn valve.
Until now the complexity of known systems has limited their application to specific fields, in particular the nuclear industry. A first objective of the invention is to simplify this type of control device using a metal bellows in order to diversify its application into other sectors of the chemicals industry. The invention is particularly directed to the operation of a quarter-turn valve by means of a bellows type sealed transmission device in which the aforementioned "circular-translation" movement is generated positively by an appropriate kinematic system of simple design.
The basic idea of the invention, from which the structural simplification results, consists in physically offsetting the control shaft and the receiver shaft by placing the axes of these two shafts at the ends of one side of a deformable parallelogram type articulaion system including said transfer member.